The present invention relates to industrial controller systems used for real-time control of industrial processes, and in particular to an interface module for use with such industrial controller systems providing direct access to input and output points of the control system over the World Wide Web.
Industrial control systems are special purpose computer systems used in controlling industrial processes. Under the direction of a stored control program, a programmable logic controller, being part of the industrial control system, reads inputs from a series of input modules and writes outputs to a series of output modules. The input modules read signals from sensors associated with the industrial process and the output modules provide signals to actuators and the like in the industrial process. The inputs and outputs may be binary, that is on or off or analog, providing a value with a continuous range such as, for the case of inputs, from an analog to digital converter or an encoder.
Industrial control systems differ from conventional computer systems in that they provide highly reliable operation and deterministic real-time control. In part, this requires both that data communicated between the programmable logic controller and the input and output modules be transmitted in a predictable sequence. This may be provided by use of an I/O image table which is populated with complete sets of input or output data before control decisions are made and before outputs are forwarded to the I/O modules.
It is also necessary that data be reliably transmitted between the programmable logic controller and the I/O modules within predictable and short time limits. One way this may be provided by using a network supporting “connected messaging”. In connected messaging, communicating devices of the system establish a “connection” prior to the transmission of data. The process of establishing the connection reserves the necessary network bandwidth, buffer space, and other network resources on the end nodes and along the way between them via connecting media and intervening devices such as bridges, or routers. When messages are sent, reliable transmission can thereby be assured.
A number of connected messaging systems are well known in the art including Control Net, a network supported by the Allen-Bradley division of Rockwell, as well as DeviceNet and a number of other well known networks.
An important component of an industrial control system is the human machine interface (HMI) which allows, testing, troubleshooting and monitoring of the industrial process. Typically HMIs read and write to the I/O image table of the programmable logic controller under the operation of the control program.
Often it is desired to monitor an industrial process remotely. The development of the Internet and the Web has raised the possibility of using well known remote communication techniques with Web servers and browsers to implement a remote HMI that could be used on any browser enabled computer. Current proposals for providing Web to an industrial control system envision a Web server module that may plug into a common backplane to communicate with the programmable logic controller. Input and output data is communicated between the I/O module and the programmable logic controller and selectively communicated, under the control of the programmable logic controller, between the programmable logic controller and the Web server module.